Photographic negatives and their preparation



United States Patent 3,129,096 PHOTOGRAPHIC NEGATIVES AND THEIR PREPARATION James Archibald Co-liinson, Middletown, and Robert William Nottorf, Westiield, N.J., assignors to E. I. du Pont de Nemonrs and (Iompany, Wilmington, Del., a corporation of Delaware No Drawing. Filed Jan. 27, 1960, Ser. No. 4,891 11 Claims. (Cl. 96-47) This invention relates to photographic elements and their preparation. More particularly, it relates to a process for the preparation of high-contrast photographic negatives. Still more particularly, it relates to the preparation of photographic negatives from relief printing forms by the transfer of a dry opaque material to high-contrast photographic films.

Many techniques have been developed for the preparation of negatives from printing plates and engravings. These techniques, however, are time consuming and costly. The most commonly used conversion methods include:

(1) Opaque repro proofAn ink impression of the relief printing form is made on paper and the printed image is photographed in a process camera to yield a nega tive image corresponding to the relief surface. To prepare a right-reading negative two additional contact photographic steps are required or the image reversal must be accomplished optically in a camera. The process suffers from loss of fidelity due to ink squeezeout during the printing of the proof. Ink squeezeout results in the tendency of characters to be slightly bolder than the original, i.e., the wet ink is physically squeezed out when the hard paper surface is printed with the printing form.

(2) Transparent repro proofThis technique is sililar to the opaque repro proof method described above except that the image is printed on thin, transparent plastic, e.g., cellophane. The print is a transparent positive of the relief surface. Only contact photography is involved to obtain a negative but ink squeezeout remains a problem.

(3) Ink impression on a photographic filmThe printing relief is coated with ink and while wet this is printed onto the emulsion side of a photographic film. The inked material acts as a light stencil or development resist. One of the main problems encountered with this method is ink squeezeout due to the hard emulsion surface. This causes portions of the areas desired to be printed to have little or no ink and it further causes the squeezed-out ink to run beyond the desired printing area. The net result is poor quality and fidelity. Other problems with this method include incomplete transfer of the ink from the printing relief to the film. This Wet inked surface is also inherently harded to keep free from dust.

(4) Brightype photography (Ludlow-Typograph Co., 2032 Clybourn Avenue, Chicago 14, Illinois)A relief plate is completely blackened by coating with carbon black. The printing surface is then cleaned to expose the metal relief image, and the treated plate is photographed with a camera fitted with a broad light source designed to eliminate specular reflection. The resulting positive is used to make a contact negative. Fidelity by this process is reported to be excellent if care is taken in preparing the forms. The process has been described in the periodical, Book Production, July 1958. US. Patents 2,609,293; 2,704,410 and 2,751,294 issued to G. L. Morrison describe this process of equipment.

An object of this invention is to provide improved photographic elements and a process for their preparation. A further object is to provide an improved method for the preparation of high-contrast photographic negatives having high fidelity and equality from a relief printing plate. A still further object is to provide photographic films suitably coated so as to facilitate the production of high-contrast, right-reading photographic negatives from a relief printing plate. Other objects will appear hereinafter.

These and other objects are accomplished by the instant invention which includes an improvement in a process for preparing a high-contrast, photographic negative which comprises the steps in combination of contacting a heated printing form whose relief surface is coated with a layer of dry pigment, with a high-contrast silver halide emulsion photographic film at least one of whose sides has been overcoated with a layer of thermoplastic, solvent-soluble polymeric composition, thereby depositing said pigment on only one of said overcoated sides of said film, exposing the side of said film having the pigment deposited thereon to a light source, processing said film which includes the steps of developing, fixing and removing the pigment and overcoating layer with a solvent for said overcoating layer, the removal of said over-coating layer being carried out at any stage prior to completion of processing.

A particular embodiment of the invention is illustrated by a process for preparing a high-contrast, right-reading photographic negative which comprises the steps in combination of coating the relief surface of a relief printing form with a layer of finely divided pigment, e.g., carbon black, heating said engraving, and subsequently bringing the dry pigmented relief surface of said engraving into contact, under safe-light conditions, with the emulsion side of a high-contrast photographic film, e.g., a lithographic film coated with a gelatino-chlorobromo silver halide emulsion and which may or may not have antihalation and antiabrasion layers, said film being overcoated with a layer of a thermoplastic, solvent-soluble polymeric composition. While still warm, the photographic film is removed from the pigmented surface. A pigmented image is thereby transferred to the surface of the photographic film. The film is exposed to a light source so that a negative latent image of the transferred opaque pigment image is formed in the photographic emulsion layer, the pigment and thermoplastic polymer on the film surface are removed by Washing in a suitable solvent and the film is developed and fixed. The highcontrast, high-quality right-reading negative obtained can then be used to prepare photopolymerizable printing elements with relief images equivalent to those of the original metallic engraving. A right-reading negative is one in which the negative image can be read normally, i.e., from left to right, when the sensitized surface of the negative is held toward the viewer.

A photographic film, preferably a high-contrast lithographic film, e.g., a lithographic film coated with a gelatino-chlorobromo silver halide emulsion which may be overcoated with a gelatin antiabrasion layer with or without a matting agent, e.g., silica, is overcoated under safelight conditions with a layer of a thermoplastic polymen'c composition having a coating weight of about 1 to 50 mg./dm. preferably a water-soluble, high molecular weight polyethylene oxide (average molecular weight of 50,000 or more). The relief surface of a printing form, e.g., a copper engraving, is coated with a layer of pigment, preferably carbon black, by passing the surface of the printing form through a sooty flame, and the printing form is heated to a temperature of about 50 to 180 C., preferably 70 to 80 C. The thermoplastic coated photographic film is brought into intimate contact with the heated printing form, and while still warm, the surfaces are separated. The duration of contact between the film and the printing form is generally a few tenths of a second. A pigmented image of the relief is transferred to the surface of the photographic film, and said film is then given an exposure to light, preferably a broad light source, predetermined to give a developed optical density of 3.5. The thermoplastic composition and pigment are removed by washing the film in a suitable solvent, preferably tap water, the film is developed in a standard Litho-type developer solution, and the image is fixed.

The invention will be further illustrated but is not intended to be limited by the following examples which were conducted under safelight conditions:

Example I A 4-inch by -inch high contrast lithographic film coated with a gelatino-chlorobromossilver halide emulsion and overcoated with a gelatin antiabrasion layer containing silica (7 microns in diameter) was overcoated with an aqueous solution of low viscosity polyethylene oxide, average molecular weight of 100,000 (3 percent solids by weight), containing 0.2 percent solids by weight of sodium lauryl sulfate to give a dry coating Weight of 30 mg./dm. The film was attached by means of adhesive tape, emulsion surface out, to a cylinder, 8 inches in diameter and 12 inches in length and weighted to 16,783 grams. The cylinder had been covered first with a 6-inch wide rubber pad, A inch in thickness, and then with a 6-inch wide sheet of manila paper, 0.006 inch in thickness. A copper photoengraving which contained representative samples of many types of printing structures, e.g., pictures and letter text including halftone dot and line images, was coated with a thin layer of carbon black by passing the engraving through a sooty fiame until the plate surface became a dark brown. A protective cover of cardboard was placed over, bu-t not in contact with, the pigmented engraving to protect its surface from dust, etc. The protective-covered engraving was placed on a hot plate for 5 minutes at a temperature of 76 C. The lithographic film, overcoated with polyethylene oxide, was dusted with a static brush and then was rolled across the pigmented surface of the uncovered engraving. Carbon black adhered to the polyethylene oxide coating on the lithographic film in the areas corresponding to the printing surfaces of the photoengraving. The lithographic film with the carbon black adhering in the contact areas was exposed to a point light source with an intensity and time predetermined to produce a developed optical density of 3.5 in the non-image areas. The exposed film was then washed with cold tap water to remove the carbon black and the polyethylene oxide coating. The film was subsequently developed at 20 C. for 2% minutes in the following solution:

Water (32 C.) ml 500.0 Sodium sulfite, anhydrous g 30.0 Paraformaldehyde g 2.2 Boric acid, crystals g 7.5 Hydroquinone g" 22.5 Potassium bromide g 1.6 Water to make 1.0 liter.

The film Was fixed for 5 minutes at 20 C. in the following solution:

Water (15 C.) rnl 600.0 Sodium thiosulfate, anhydrous g 153.0 Sodium sulfite, anhydrous -g- 15.0

4 Sodium borate g 18.0 Potassium alum g 20.0 Glacial acetic acid ml 12.0

Water to make 1.0 liter.

The high-contrast negative obtained was an excellent right-reading reproduction of the original engraving. Upon drying, the negative was used to expose a photopolymerizable printing element prepared as described in Example 3 of assignees Burg application, Serial No. 750,868, filed July 25, 1958. On processing, an excellent printing plate reproduction of the original engraving was obtained.

Example II A 4-inch by 10-inch high-contrast lithographic film similar to that described in Example I was coated with a thin layer of polyethylene oxide, average molecular weight of 100,000, as described in Example I. The film was attached to the cylinder as described in Example I except that the cylinder was weighted to 10,200 grams. A copper engraving as described in Example I was dusted on its printing surface with finely divided particles of carbon black (particle size 73 mg). The pigment-dusted engraving was placed on a fiat hot plate at a temperature of 70 C. The cylinder with the film attached was rolled across the pigmented surface of the engraving. The dusted carbon black adhered to the polyethylene oxide coating on the lithographic film in the areas corresponding to the printing surfaces of the photoengraving. The photographic film was placed in a viewing box containing a broad light source with the emulsion coating of the film substantially in contact with the plane glass of the light source. A piece of non-reflective, weighted black velvetone was placed on the back of the film to insure contact of the film with the glass. The film was exposed with an intensity and time predetermined to produce a developed optical density of 3.5 in the non-image areas. Upon removal of the film, the carbon black and polyethylene oxide coating were washed away with tap water, and the film was developed at 20 C. for 2% minutes in the developer described in Example I. The right-reading negative image was fixed in the fixer solution as described in Example I. A satisfactory, high-contrast rightreading negative of the original engraving was obtained.

Example III A lithographic photographic film overcoated with a thin layer of polyethylene oxide, average molecular weight of 100,000, was prepared as described in Example I, and the film was attached to the cylinder described in Example II. The copper engraving described in Example I was completely coated with a layer of magnesium oxide by burning magnesium metal. The heated, pigmented relief surface was brought into intimate contact with the polyethylene oxide coated film as described in Example II and the surfaces were stripped apart. The film was exposed to a point light source of the type for microscopic illumination supported about 4 feet distant from the film. The intensity and time of exposure were predetermined to produce a developed optical density of 3.5 in the nonimage areas. The magnesium oxide pigment and the polyethylene oxide coating were removed by washing with tap water as described in Example II and the film was developed and fixed as described in Example I. A satisfactory, high-contrast right-reading negative of the original engraving was obtained.

Example IV A high-contrast lithographic film described in Example I except that the film had no antiabrasion layer was coated as described in that Example on both sides of the film with the polyethylene oxide, average molecular weight of 100,000. The thermoplastic coating was allowed to dry, and the film was attached emulsion side down by beans of adhesive tape to the cylinder described in Exam-- ple II. The polyethylene oxide coated base surface was rolled over the sooted, carbon black surface of the copper engraving prepared as described in Example I. The carbon black adhered to the thermoplastic coating on the film base in the areas corresponding to the engraving printing surfaces. The film was removed from the cylinder and was exposed through the base side of the film to the distant point source described in Example III. The intensity and time of exposure were predetermined as described in Example III. The film was washed in cold tap water, developed and fixed as described in Example I. A high-contrast negative was obtained which was an excellent wrong-reading reproduction of the original engraving. The wrong-reading negative was used to prepare a lithographic printing plate.

Example V Fifteen grams of Carbowax 20 M, a polyethylene glycol manufactured by Union Carbide Corporation,

New York 17, New York, having an estimated molecular Weight of 15,000 to 20,000, a viscosity (25 weight percent in water) at 210 F. of 57.3 centistokes, a surface tension (50 weight percent aqueous solution) at 40 C. of 40.7 dynes/cm. and a refractive index at 40 C. of 1.459, were added with stirring to 450 ml. of water in a dish, and the stirring was continued until the solid dissolved. To the aqueous solution were added 7.5 ml. of an aqueous solution of an anion-active surfactant, Triton X200, sodium p-l,1,3,3-tetramethylbutyl phenoxy polyethoxyethyl sulfonate (manufactured by Rohm & Haas Co., Philadelphia 5, Pa.) and water to make 500 ml. A 4-inch by 10-incl1 high-contrast lithographic film coated on one side with a gelatino-chlorobromo silver halide emulsion, and on the other side with an antihalation layer was dip-coated in the polyethylene glycol solution described above. The film was allowed to drain for 5 minutes and was then placed in a drying oven at 95 C. for 30 minutes. The film was attached, emulsion surface exposed, to the cylinder described in Exam le II. The copper engraving described in Example I was coated with carbon black from a sooty flame as described in the example. The pigmented plate was then heated on a hot plate to a temperature of about 96 C. and the photographic film was rolled over the pigmented engraving surface, the carbon black adhering to the film surface in the areas that were brought into contact with the printing images of the engraving. The photographic film was exposed as described in Example III to the point light source described in that example. Prior to development the carbon black and thermoplastic coating were removed by washing the film in tap water. The film was then developed and fixed as described in Example I. An excellent high-contrast right-reading negative of the original engraving was obtained.

Example VI A 4-inch by -inch high-contrast lithographic film as described in Example V was dip-coated in an ethanol solution containing g. of polyvinylpyridine and to which had been added 7.5 ml. of the anion-active surfactant described in Example V (the total amount of solution was 500 ml). The film was allowed to drain and was dried in an oven for 30 minutes as described in Example V. The film was attached as described in Example II to the cylinder described in that example and was rolled over the carbon black pigmented engraving prepared as described in Example I but which had been heated to 93 C. The lithographic film was exposed as described in Example III to the point light source described in that example. The film was washed in ethanol and the polyvinylpyridine subsequently was peeled off. The film was developed, and the image was fixed as described in Example I. A satisfactory high-contrast right-reading negative of the original engraving was obtained.

-source described in that example.

6 Example VII A 4-inch by 10-inch high-contrast lithographic film as described in Example V was dip-coated in an aqueous solution containing 15 g. of polyvinylpyrrolidone and to which had been added 7.5 ml. of the anion-active surfactant described in Example V (the total amount of solution was 500 ml.). The film was allowed to drain and was dried as described in Example V. The film was attached emulsion surface out, to the cylinder described in Example II and was rolled over a heated, carbon black pigmented copper engraving prepared as described in Example I. Carbon black adhered to the thermoplastic coated surface of the lithographic film in the areas that were brought into contact with the engraving printing surfaces. The film was then exposed as described in Example III to the point light source described in that example and was placed in the developer described in Example I for 5% minutes. The image was fixed for 4 minutes in the fixer solution described in Example I and was then washed in water at 20 C. The carbon pigment was rubbed off the negative surface. A satisfactory right-reading negative of the original engraving was obtained.

Example VIII A 4-inch by IO-inch high-contrast lithographic film, as described in Example V, was coated by dipping into an aqeous solution containing 20 ml. of Elvacet 81- 900, a dispersion of polyvinyl acetate in water manufactured by E. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware, said dispersion is a viscous, milkwhite liquid containing 55 to 57 percent solids, has a Brookfield viscosity of 800 to 1,000 centipoises, a pH of 4 to 6 and contains less than 1 percent vinyl acetate monomer, which was thoroughly dispersed by stirring in distilled water. Fifteen m1. of the anion-active surfactant described in Example V and water were added to make 500 ml. The film was allowed to drain and was dried as described in Example V. The film was attached with its emulsion surface out to the cylinder described in Example 11 and was rolled over a heated (96 C.), carbon black pigmented copper engraving prepared as described in Example I. The film was removed and was exposed as described in Example III to the point light The film was then placed in the developer solution described in Example I for 2 /2 minutes. The image was fixed by the procedure described in Example VII. The thermoplastic coating and carbon black areas were removed from the negative surface by rubbing the surface in water at 20 C. A

satisfactory right-reading negative of the original engraving was obtained.

Example IX Fifteen grams of Tergitol Nonionic XI-I, a white solid polyalkylene glycol ether manufactured by Union Carbide Corporation, New York 17, New York, which is completely soluble in water, has a pH (0.1% aqueous solution) of 6.0, a specific gravity of 1.0344 at 70/20 C. and an apparent viscosity at 70 C. of 230 centistokes and at 105.4 C. of 58.1 centistokes, was added with stirring to 450 ml. of distilled water until all the solid dissolved. Seven and one half cubic centimeters of the anionic-active surfactant, described in Example V, were added to the solution, and the total amount of solution was brought up to 500 ml. by adding additional water. A 4-inch by 10-inch high-contrast lithographic film as described in Example V was dip-coated in the polyalkylene glycol ether solution. The film was allowed to drain and the coating was dried as described in Example V. The dry film was attached to the cylinder described in Example II and was rolled over the carbon black pigmented surface of the copper engraving described in Example II which had been heated to 96 C. The film was exposed as described in Example III to the point light source described in that example.

The film was developed for minutes in the developer described in Example I and the image was fixed for 4 minutes in the fixer solution described in that example. The fixed negative was washed in tap water at C. and the carbon was rubbed off the surface. A satisfactory right-reading negative of the original engraving was obtained.

High-contrast photographic films bearing overcoatings, Which transmit some light actinic to the film, which are adhesive or which can be made adhesive at the time of contact with the surface of the printing relief, and which are readily removed from said film surface, are useful in the present process.

Useful photographic films include all high-contrast or lithographic type films, preferably lithographic films having gelatino-silver halide emulsions (e.g., silver chlorobromide emulsions). Other high-contrast silver halide photographic films also may be used, e.g., those having binders of polyvinyl alcohol, polyhydroxyalkane (5 to 10% of the polymerizable groups being ethylene groups), synthetic amphoteric polymers of Shacklett US. Patents 2,777,872, 2,830,972, 2,834,758 and 2,846,417, etc. These films can be overcoated with antihalation and antiabrasion layers such as are known to the art. The antiabrasion layers can contain a matting material, e.g., silica, starch, magnesium silicates, etc. The above-described antihalation and antiabrasion overcoatings, however, are not a critical constitutent of the photographic film. In its preferred form, the photographic film has no antihalation backing, but generally, a light absorptive material is placed against the back of the film during exposure.

The photographic film is overcoated with a material that is adhesive or can be made adhesive, e.g., by heating, moistening or by appropriate chemical treatments. In addition, the overcoating must transmit some light actinic to the film and be readily removed by an aqueous solution or solvent which has no deleterious effect on the emulsion coating of the photographic film.

The preferred overcoating material is a high molecular weight polyethylene oxide having a molecular weight of at least 50,000. The polyethylene oxides are thermoplastic, form transparent films which have a hard, smooth, non-tacky surface at normal room temperature, but become tacky and adhesive when heated to a temperature of about 55 to 150 C. In addition, the polyethylene oxide coating has no deleterious effect on the sensitometry of the emulsion coating of the photographic film and is soluble in cold Water.

Other thermoplastic polymeric overcoating compositions are useful but do not possess all the enumerated advantages of the high molecular weight polyethylene oxide overcoatings. Illustrative of useful overcoating materials which possess essentially all the advantages of the preferred polyethylene oxides, but which are not water-soluble are: polyvinyl acetates; polyvinylpyridines; copolyesters, e.g., those prepared from the reaction product of a polymethylene glycol of the formula HO (CH OH where n is a whole number of from 2 to 10 inclusive, and (l) hexahydroterephthalic, sebacic and terephthalic acids, (2) terephthalic, isophthalic and sebacic acids, (3) terephthalic and sebacic acids, and (4) terephthalic and isophthalic acid; mixed cellulose esters, e.g., cellulose acetate succinate, cellulose acetate butyrate; poly- (vinyl acetate/crotonic acid); polyvinyl acetals, e.g., polyvinyl butyral, polyvinyl formal; cellulose ethers, e.g., methyl cellulose, ethyl cellulose.

The following polymeric compositions are Water-soluble but do not possess at least one of the other advantages possessed by polyethylene oxide: polyethylene glycols, e.g., average molecular weight of 1,000 to 24,000 (the surface is soft at normal room temperature); polyalkylene glycol ethers; and polyvinylpyrrolidones.

It has been found that the adhesion of the above polymers to the photographic film can be improved by the addition of a surface active agent, e.g., sodium lauryl sulfate, cetyl betaine, cetyl pyridinium chloride, etc., to the thermoplastic polymer solution.

Other substances which are useful as the overcoating layer of the high-contrast photographic film but which are generally non-thermoplastic and do not possess all the advantages of the preferred overcoating composition include: substances which can be made adhesive by moistening with solvents such as water, alcohol, ketones, etc., e.g., carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylamide, polyvinyl alcohol, casein, agar agar, dextran, and those substances which are adhesive at room temperature and which are applied to the photographic film immediately prior to use, e.g., rubber cement, glues of various types, etc. Care must be taken not to expose any of the adhesive coatings so that dirt, dust, etc. adheres to the coating. Protective covers, e.g., films of polyethylene terephthalate or other plastics, paper, cardboard, and the like, may be used to cover the coated surface of the film prior to the contact operation. The covers should not touch the adhesive surface.

The printing forms to be copied are coated with a pigment layer. Suitable printing forms include those made from metals; e.g., copper, zinc, aluminum, magnesium, steel, nickel, chrome, brass, type metal; plastics; rubber, etc. Any type of image on said forms can be copied, e.g., solids, reverses, text, line work, halftones, etc.

Pigments which can be applied to the printing form face, in addition to the preferred carbon black, include magnesium oxide, the black and red forms of iron oxide, manganese dioxide, finely divided metals such as aluminum and copper, phthalocyanines, and azo-pigments.

The pigments can be applied as powders by dusting on or they can be in the form of liquid dispersions or aerosols and rolled or sprayed onto the engraving. The preferred method of applying the carbon black pigment is by means of a sooty flame. Other means of application known to the art are also useful provided the pigment coating is opaque, finely divided and is non-cohesive.

The pigmented printing forms and overcoated photographic film must be brought into intimate contact to insure the transfer of the pigment in the image areas to the photographic film when the said surfaces are separated. Preferably the film is mounted on a cylinder such as is described above in the examples. The weight of the cylinder can be adjusted to apply pressure to insure adequate surface contact. The film can be fastened to the cylinder by means of a standard adhesive tape or other means known to the art. The film, however, can also be mounted on a flat surface and brought into intimate contact with the printing form surface by means of static pressure or the system can be placed in a vacuum frame. The pressure applied will vary with the particular printing form used and preferably is kept as low as is consistent with complete transfer.

When the thermoplastic compositions which are nontacky at room temperature are used, it is necessary, to insure complete transfer of the pigment in the relief image areas, to heat either the printing form, the film support or both. Preferably, however, the form surface is heated. Heat can be applied by means well known in the art, e.g., rollers, flat heating surfaces, radiant sources, e.g., heating lamps, etc. The heating temperature in general may fall in the range over which the thermoplastic coating is tacky, e.g., 50 C. and higher, but preferably is kept below C. The transfer preferably is accomplished in subdued light, i.e., under safe-light conditions. By use of a photographic film with a low emulsion speed, however, ordinary light can be used.

Any light source known to the art can be used to expose the high-contrast, pigmented photographic film. A geometrically broad exposure to light is preferred, however, since the positive image of the pigmented photographic film tends to be slightly bolder than the printing form image. Using the broad light source exposure, the substantial intensity of radiation at grazing incidence produced by said exposure will yield image silver in the negative in a narrow annulus just within the periphery of the positive pigment image. The boldness of the positive image can therefore be corrected in the negative. For convenience, the intensities and exposure times of the light sources used are predetermined to produce a developed optical density of 3.5 in the nonimage areas. This developed optical density is not a critical part of the present invention, however, as developed optical densities above and below 3.5 can be used and good results obtained. Optical densities in the range of 3.0 to 3.5 and more are preferred.

Any solvent that does not afiect the gelatino-emulsion surface of the photographic film can be used to remove the adhesive layer and the transferred pigment. The particular solvent, of course, depends on the type of adhesive and pigment material used. Water is preferred as the solvent, i.e., when high molecular weight polyethylene oxide is used, but ethanol and other organic solvents fulfill the above criteria. The removal of the adhesive or thermoplastic layer and pigment which is considered as part of the film processing step (together with developing and fixing) may be carried out at any stage prior to the completion of processing. For example, the removal of the adhesive and pigment may take place prior to, during and after developing and fixing.

Standard developers and fixers known to the art can be used in the present process but are restricted by the particular photographic film used.

The present invention is useful in preparing good-quaL ity, high-contrast photographic negatives from existing relief printing forms. The negative images so formed are useful as image transparencies in the exposure of photopolymerizable printing elements such as are described in Plambeck US. Patent 2,791,504. The negative images are also useful in lithographic printing and for the preparation of slides. A reproduction of the original engraving can be prepared by use of the rightreading negative prepared as described in the present invention.

The instant invention is advantageous because excellent photographic negatives can be produced which meet the stringent fidelity requirements for negatives used by the printing industry and in particular for the exposure of photopolymerizable printing plates. The negatives prepared match the original halftone relief image, on the average, within 0.0001 inch on the radius and have a transmission density in the printing areas well below 0.1.

The negatives can be prepared in less than 15 minutes by this simple and inexpensive method and are not limited by the type of relief image printing form that can be used.

The process is particularly advantageous when the photographic film is overcoated with a high molecular weight thermoplastic polyethylene oxide composition. At room temperature the thermoplastic material is hard and slick and the film is easily handled. Only upon the application of heat at the time of impression of the pigmented surface does the thermoplastic material become tacky, i.e., the tendency to pick up dust and dirt particles is greatly reduced. The polyethylene oxide and pigment are easily removed after exposure of the photographic film with water.

What is claimed is:

1. A process for preparing a photographic negative utilizing a relief printing form which comprises the steps in combination of contacting a heated printing form whose relief surface is coated with a layer of dry pigment, with a high-contrast silver halide emulsion photographic film at least one of whose sides has been overcoated with a layer of thermoplastic, solvent-soluble polymeric composition, said composition being relatively non-adhesive at normal room temperature, being insensitive to light and being capable of transmitting some light actinic to said silver halide emulsion, thereby depositing said pigment on only one of said overcoated sides of said film, exposing the side of said film having the pigment deposited thereon to a light source, processing said film which includes the steps of developing, fixing and removing the pigment and overcoating layer with a solvent for said overcoating layer, the removal of said overcoating layer being carried out at any stage prior to completion of processing.

2. A process for preparing a right-reading photographic negative utilizing a relief printing form which comprises the steps in combination of overcoating the emulsion side of a gelatino-silver halide emulsion photographic film with a layer of a thermoplastic, solvent-soluble polymeric composition, said composition being relatively non-adhesive at normal room temperature, being insensitive to light and being capable of transmitting some light actinic to said silver halide emulsion, providing a layer of dry, opaque finely divided pigment on the relief surface of said printing form, heating said form to a temperature of from about 50 to C., contacting said relief surface with said overcoated side of said film thereby depositing said pigment from said relief surface onto said overcoated side of said film, exposing the overcoated side of said film to a light source, processing said film which includes the steps of developing, fixing and removing the pigment and overcoating layer with a solvent for said overcoating layer, the removal of said overcoating layer being carried out at any stage prior to completion of processing.

3. Process according to claim 2 wherein said removal of said overcoating layer is conducted prior to developing and fixing.

4. Process according to claim 2 wherein the polymeric composition is a water-soluble polyethylene oxide having an average molecular weight of at least 50,000, the solvent therefor being water, and the pigment is carbon black.

5. Process according to claim 2 wherein the layer of thermoplastic, solvent-soluble polymeric composition has a coating Weight of from 1 to 50 mg./dm.

6. Process according to claim 2 wherein the polymeric composition is a polyethylene glycol of an average molecular weight of about 1,000 to 24,000, and the solvent therefor is water.

7. Process according to claim 2 wherein the polymeric composition is polyvinylpyridine.

8. Process according to claim 2 wherein the polymeric composition is polyvinylpyrrolidone.

9. Process according to claim 2 wherein the polymeric composition is a water-soluble polyalkylene glycol ether.

10. A process for preparing a wrong-reading photographic negative utilizing a relief printing form which comprises the steps in combination of overcoating the base side of a gelatino-silver halide emulsion photographic film with a layer of a thermoplastic, solvent-soluble polymeric composition, said composition being relatively non-adhesive at normal room temperature, being insensitive to light and being capable of transmitting some light actinic to said silver halide emulsion, providing a layer of dry, opaque finely divided pigment on the relief surface of said printing form, heating said form to a temperature of from about 50 to 180 C., contacting said relief surface with the overcoated side of said film thereby depositing said pigment from said relief surface onto said overcoated side of said film, exposing the photographic film through the overcoated base to a light source, processing said film which includes the steps of developing, fixing and removing the pigment and overcoating layer with a solvent for said overcoating layer, the removal of said overcoating layer being carried out at any stage prior to completion of processing.

11. Process according to claim 10 wherein said removal of said overcoating layer is conducted prior to developing and fixing.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Capstafi May 13, 1919 Swaim July 23, 1929 Sheppard et a1 June 10, 1930 Heineske May 30, 1933 Staud Apr. 10, 1934 Hrauska Aug. 18, 1936 Bronfman Dec. 3, 1940 Lindquist June 15, 1943 12 Blake et a1 July 8, 1947 Blake May 11, 1948 Kendall Nov. 29, 1955 Weigel July 2, 1957 Pajes July 15, 1958 Dersch Oct. 31, 1961 OTHER REFERENCES Hill: High Molecular Weight Polymers of Ethylene Oxide, Industrial and Engineering Chemistry, vol. 50, No. 1, January 1958, pp. 5-16. 

1. A PROCESS FOR PREPARING A PHOTOGRAPHIC NEGATIVE UTILIZING A RELIEF PRINTING FORM WHICH COMPRISES THE STEPS IN COMBINATION OF CONTACTING A HEATED PRINTING FORM WHOSE RELIEF SURFACE IS COATED WITH A LAYER OF DRY PIGMENT, WITH A HIGH-CONTRAST SILVER HALIDE EMULSION PHOTOGRAPHIC FILM AT LEAST ONE OF WHOSE SIDES HAS BEEN OVERCOATED WITH A LAYER OF THERMOPLASTIC, SOLVENT-SOLUBLE POLYMERIC COMPOSITION, SAID COMPOSITION BEING RELATIVELY NON-ADHESIVE AT NORMAL ROOM TEMPERATURE, BEING INSENSITIVE TO LIGHT AND BEING CAPABLE, OF TRANSMITTING SOME LIGHT ACTINIC TO SAID SILVER HALIDE EMULSION, THEREBY DEPOSITING SAID PIGMENT ON ONLY ONE OF SAID OVERCOATED SIDES OF SAID FILM, EXPOSING THE SIDE OF SAID FILM HAVING THE PIGMENT DEPOSITED THEREON TO A LIGHT SOURCE, PROCESSING SAID FILM WHICH INCLUDES THE STEPS OF DEVELOPING, FIXING AND REMOVING THE PIGMENT AND OVERCOATING LAYER WITH A SOLVENT FOR SAID OVERCOATING LAYER, THE REMOVAL OF SAID OVERCOATING LAYER BEING CARRIED OUT AT ANY STATE PRIOR TO COMPLETION OF PROCESSING. 